Currently, in the world, energy is used mostly in the form of fossil fuel, atomic power, water energy etc. in an irreversible manner. Especially, the consumption of fossil fuel is a factor for accelerating global warming and environmental disruption. Accordingly, development has advanced for so-called clean energy lowering the load on the environment, by the use of solar energy generation, wind power generation, or hydrogen gas. However, the development of clean energy is still in a nascent stage, and there still remains a considerably long way to go until the use as a substitute for fossil fuel and atomic energy.
Although thermal energy exists inexhaustibly in the natural world, on the other hand, the technique to take out the thermal energy in the form of mechanical energy or chemical energy is not yet developed to a level of practical use. The principle of conversion from thermal energy into a directly usable form such as electric power is known as Peltier effect or Seebeck effect. That is, radiating or absorbing heat is produced other than Joule heat when current flows through conductors of two different kinds which are connected and held at a uniform temperature. This effect is the phenomenon first discovered by J. C. A. Peltier in 1834, and called Peltier effect. Moreover, when copper wires of two different kinds are connected, the two contact points are held at different temperatures T1 and T2, and one of the conductive wires is cut, then an electromotive force is produced between the cut ends. This phenomenon was first discovered by J. J. Seebeck in 1821. The electromotive force generated between the two ends is called thermal electromotive force, and this phenomenon is called Seebeck effect in honor of the discoverer.
The development of a thermoelectric converter element (Seebeck element) utilizing the Seebeck effect is attracting attention as substitute energy for fossil fuel and atomic power. The thermo-electromotive force of the Seebeck element is dependent on the temperatures of the two contact points, and moreover on the materials of the two conductor wires, and a derivative value obtained by dividing the thermo-electromotive force by a temperature variation is called a Seebeck coefficient. The Seebeck element is formed by contacting two conductors (or semiconductors) different in the Seebeck coefficient. Due to difference in the number of free electrons in the two conductors, electrons move between the two conductors, resulting in a potential difference between the two conductors. If heat energy is applied to one contact point, the movement of free electrons is activated at the contact point, but the free electron movement is not activated at the other contact point being provided with no heat energy. This temperature difference between the contact points, that is the difference in the activation of free electrons, causes conversion from heat energy to electric energy. This effect is generally referred to as thermoelectric effect.
The inventor(s) (applicant) of the present application has invented and proposed a thermoelectric conversion apparatus utilizing the Seebeck effect and an energy conversion system utilizing this (cf. patent document 1).
FIG. 13 shows as one example of the technique disclosed in the patent document 1, a thermal energy to electric energy direct conversion system. This system includes a thermal energy to electric power direction conversion section 100 converting thermal energy from a heat source directly to electric potential energy by the Seebeck effect with a circuit composed of series connected stages of thermoelectric effect elements 101, and an electrolysis section 200 disposed as a load circuit at the output voltage end, for converting to chemical potential energy by electrolysis of water.
The thermoelectric effect element 101 constituting the conversion section 100 for directly converting thermal energy to electric power by the Seebeck effect is formed by connecting first and second thermoelectric conversion elements 102 and 103. The first thermoelectric conversion element 102 is composed of first and second conductive members A102 and B102 having different Seebeck coefficients and joining member d102, and the second thermoelectric conversion element 103 is composed of first conductive member A103, joining member d103 and second conductive member B103. As shown in FIG. 13, the elements constituting the first thermoelectric conversion element 102 and second thermoelectric conversion element 103 are formed by connecting a plurality of Peltier Seebeck elements in a series form. By the use of heat energy of a heat source such as an auxiliary heater, the temperature T1 of the joining members d102 is set higher than the temperature T2 of the joining members d103. That is T1>T2.
When a switch SW shown in FIG. 13 is turned on, a current IL flows through the first and second thermoelectric conversion elements 102 and 103 alternately. The current IL flows from the first conductive member A102 through the joining member d102 to the second conductive member B102 in one of the first thermoelectric conversion elements 102; then the current IL flows from the second conductive member B103 through the joining member d103 to the first conductive member A103 of the next second thermoelectric conversion element 103; and the current IL further flows again to the part of the first thermoelectric conversion elements 102. The output terminal end is connected to the load circuit which, in this example, is the electrolysis section 200 converting to chemical potential energy by electrolysis of water. The distance between the first thermoelectric conversion elements 102 and the second thermoelectric conversion elements 103 is set at such a value as to hold the temperature state of T1>T2. This distance may be set at a value in a wide range from a very short length of about several microns, to a long length of several hundreds kilometers or more.
Patent document 1: Published Japanese Patent Application JP2003-92433A.
However, in the invention disclosed in the patent document 1, the process of producing the first and second thermoelectric conversion elements 102 and 103 requires operations of soldering first and second conductive members A and B and joining members d one by one. Therefore, a considerable time of skilled technicians is required for soldering, for example, and the production process is not efficient.